The 1973 distribution and abundance of breeding ospreys in the Chesapeake Bay

An aerial survey in association with several intensive ground surveys yielded the first estimate of the size of the osprey (Pandion haliaetus carolinensis) nesting population in Chesapeake Bay. The 1973 population was estimated at 1,450 ± 30 pairs, of which 713 were on the western shore and 737 on the eastern shore. A small percentage of nonbreeders (possibly 2-5 percent) may be included in this estimate. Only 31.7 percent of the population was nesting in trees; the remaining birds utilized duck blinds (28.7 percent), channel markers (21.8 percent), and miscellaneous man-made structures (17.8 percent). The geographical distribution of nesting ospreys has quite likely changed during the last several decades as suitable artificial nesting sites have become more available. Furthermore, limited evidence suggests that birds nesting on the man-made sites were more successful than those nesting in trees. This study provides a basis for monitoring future changes in numbers and distribution.